In what ratio must water be mixed with milk to gain 25% by selling the mixture at cost price?*1:11:61:45:1

To find the ratio in which water must be mixed with milk to gain 25% by selling the mixture at cost price, we need to understand that the gain is essentially the water that is added for free.

Let's denote:

• M as the cost price of milk per liter
• W as the cost price of water per liter (which is 0 because water is free)
• S as the selling price per liter of the mixture (which is equal to the cost price of milk, M, because we are selling the mixture at the cost price of milk)

The gain is given by the formula:

Gain = Selling price - Cost price

In this case, the gain is 25% of the cost price of milk, so:

0.25M = S - (M + W)

Since W = 0 and S = M, we can simplify this to:

0.25M = M - M

0.25M = 0

This means that the cost price of milk must be 4 times the selling price of the mixture to gain 25%. Therefore, the ratio of water to milk in the mixture must be 1:4.